AMR

To stream amr-nb with vlc to mobile-phone eg. next setting works (tested on few nokia & sony ericsson phones)

transcode{vcodec=H263,width=128,height=96,vb=28,fps="12.5",acodec=samr,ab="5.25",samplerate=8000,
channels=1,venc=ffmpeg{keyint=6,strict=1,strict-rc=1}}:rtp{mp4a-latm,port-video=2244,port-audio=2242,dst=1
27.0.0.1,ttl=12,sdp=\"file:///usr/local/movies/mobile.sdp\"}

It seems that mp4a-latm somehow affects on audio-output on amr also. AMR-NB requires 8000 samplerate and only 1 channel, also if you choose incorrect audio-bitrate, vlc gives you 'unknown codec' or similar error.

See Wikipedia on the AMR format.